Field of the Invention
The present invention relates to: a fuser control device that delivers current to a heater housed in a fusing device with a predetermined duty ratio; and an image forming apparatus.
Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
Japanese Unexamined Patent Publication No. 2009-069371 describes such an image forming apparatus as described above. In this image forming apparatus, a rectifier circuit receives alternating current from a commercial power source and converts it to direct current. An inverter circuit receives direct current from the rectifier circuit, converts it to alternating current by switching (between on and off) a switching element at a duty ratio determined by a control signal from a processor portion, and delivers alternating current to a heater. In the manner described above, the image forming apparatus controls the current delivered to the heater.
Other image forming apparatuses each are allowed to control the current delivered to a heater by a well-known chopper circuit including a switching element, a free-wheeling element (diode), and a reactor. This chopper circuit operates in continuous current mode when switching the switching element at a high duty ratio (e.g., when the image forming apparatus performs printing). In continuous current mode, reverse current flows through the free-wheeling element, and the level of terminal noise grows accordingly. The temperature of the switching element is also raised by switching loss. During this conventional current control, bulk power often fails to be delivered to the heater, and the temperature of the fusing device thus can be controlled within only a limited range.